Avoid locking profile task when it is already lock

WorkLockActivity was started repeatedly on top of the
task that contains work apps when turning screen on
and off over and over. So, lots of the WorkLockActivity
instances were created and added in the task, which
caused system sluggish.

Bug: 177457096
Test: manually test work challenges
Test: RootWindowContainerTests
Change-Id: Iac345471ef3badad6b9e5c0cc2873c60938663eb
Merged-In: Iac345471ef3badad6b9e5c0cc2873c60938663eb
(cherry picked from commit 805585ed)